1. Field of the Invention
The present invention relates to a novel amorphous divalent metal salt to shorten the setting time and improve the handling property for the Portland cements. A powder mixture consisting of hydrophilic particles including Portland cement clinker, bismuth oxide, and gypsum is extensively applied as a dental filling material. Therefore, the hydration of this dental filling material should undergo similar mechanisms as Portland cement. The endodontic applications of the amorphous metal salt illustrated below are also related. The amorphous metal salt consisting of a divalent metal ion and two independent and different organic and/or inorganic acid anions has high solubility by way of disturbing the regularity of the atomic arrangement. Furthermore, at the end of the hydration of the Portland cements, the amorphous metal salt can separate out to enhance the viscosity. It can reduce the setting time and improve the sticking together properties of Portland cements. Hence, the amorphous metal salt of the present invention can enhance the manageability of the Portland cements as well as the dental filling materials for clinic applications.
2. Description of Related Art
According to ASTM International Standard C150, Portland cements are classified into five types according to the various contents of compositions in the cements. Type I Portland cement is known as common cement; Type II Portland cement has moderate sulfate resistance and moderate heat of hydration; Type III Portland cement has relatively high early strength; Type IV Portland cement has low heat of hydration; and Type V Portland cement has sulfate resistance.
Typical type I Portland cement consists of 50% of tricalcium silicate (3CaO.SiO2), 25% of dicalcium silicate (2CaO.SiO2), 10% of tricalcium aluminate (3CaO.Al2O3), 10% of tetracalcium aluminoferrite (4CaO.Al2O3.Fe2O3), and 5% of calcium sulfate dehydrate (CaSO4, gypsum). When Portland cement powder is mixed with water, hydration reaction starts and cement hardens. The major chemical equation is represented as follows.2(CaO)3.SiO2+6H2O→(CaO)3.(SiO2)2.3H2O+3Ca(OH)2 3CaO.Al2O3+3CaO.SO3.2H2O+26H2O→6CaO.Al2O3.3SO3.32H2O
As shown in the aforementioned chemical equation, water and Ca2+ involves in the hydration reaction of Portland cement. The ratio of water to cement powder influences the dispersion of each components in Portland cement, and also relates to the forming rate of calcium silicate hydrates (C—S—H) and calcium aluminate hydrates (C-A-H), and the physical properties of hard cement.
Additives for regulating the hydration rate have been extensively investigated to improve the workability as well as the handling properties of Portland cement. It is believed that organic compounds with many OH− groups act as good retarders due to adsorption by hydrogen bonding. The retarding action on cement by poisoning the hydrate nuclei or by blocking the water molecules is further classified in terms of four different theories, namely, precipitation, nucleation, complexation, and adsorption. In the cement literature, the hydration retarders include various metal gluconates, dextrins, high dose (0.2˜0.4 wt %) citric acid, α-hydroxy carboxylic acids, sucrose, and calcium sulfate. On the other hand, C—S—H gel and calcium hydroxide evolve by crystallization after hydration reaction. An additive-mediated nucleation and growth mechanism governs the crystallization process and results in accelerating the setting reaction. Typical accelerators include glucose, low dose (0.1 wt %) citric acid, lactic acid, calcium formate, and calcium chloride.
Currently, rapid hardening cement is developed to meet the requirement of short setting time. The rapid hardening cement can be manufactured by sintering limestone and bauxite to produce cement clinker, followed by finely grinding the cement clinker into powder. Alternatively, the rapid hardening cement can be manufactured by adding additive into Portland cement to accelerate the hardening process after the hydration reaction of the Portland cement. In 1996, U.S. Pat. No. 5,554,218 disclosed that the hydration reaction can be accelerated by adding CaCl2 with diameters of 2,250 μm or less into Portland cement to shorten the setting time. In addition, U.S. Pat. No. 5,792,252 disclosed that alkali metal carbonate is added into the cement to accelerate cement hardening process, and the initial setting time of cement can be reduced to 35˜145 min.
U.S. Pat. No. 5,605,571 disclosed an additive without chloride and nitrite, which comprises 1˜35% of alkanolamine, 1˜20% of thiocyanate, 1˜25% of carboxylic acid, and 1˜40% of a component comprising nitrate, sulfite, or a combination thereof. The initial setting time of Portland cement can be shortened to 120˜150 min by adding the additive illustrated above into the Portland cement.
In clinic, the inflamed tissues are in an acidic environment, which has a pH value reduced from 7.35 of the normal tissues to 5.6. The hydrated Portland cement has high alkalinity (about pH 12) and is a fine solid filling structure, which is a suitable biomaterial, and can be used as a dental material to seal the roots and ease symptoms of inflammation. However, the clinical use and need for Portland cement are different from those for the architecture. Therefore, there is a necessity for developing a product using Portland cement, which can meet the demands for clinical use.
In clinic, tooth cavities and root canal fillings are common dental problems. Endodontic treatment is a method, which treats diseased pulps and root ends by pulp capping, pulpotomy, or root filling to seal the affected parts. That can prevent inflammation cased by bacteria infection, and heal the tissues around the roots. In dental clinic, there are various kinds of filling materials used in endodontic treatment. Among these materials, most of them are tried to seal the root canals and the root ends, or fill the canals between periodontal tissues. The examples of the filling materials are amalgam, gutta percha, Cavit, IRM, Super EBA, composite resin, and glass ionomer cement. However, the aforementioned filling materials have problems in microleakage, cytotoxicity, poor handling property, and moisture sensitivity. Hence, these materials are not ideal filling materials for retrograde filling or perforation repairing.
Ideal filling materials should have the characteristics of good filling property, good biocompatibility, and simple clinical handling. Also, ideal filling materials should meet the demands for stable volume, undissolvable property, no interaction with tissue fluid, and also have the character of radiopacity.
Among the dental filling materials used in the endodontic treatment, mineral trioxide aggregate (MTA) developed by Dentsply Co. has the properties of high alkalinity, good sealing property, margin sealing, biocompatibility, and inducing cytokine release. The MTA can be widely used in the endodontic treatment, such as the root-end filling, repair of root and furcation perforation, pulp capping, pulpotomy, and apexification.
Mineral trioxide aggregate, called MTA, is an aggregate of mineral oxides for sealing roots and root-ends, or filling canals between periodontal tissues by Lee et al. at Loma Linda University in 1993. The main component of MTA is tricalcium complex powder comprising calcium oxide and calcium silicate. The mineral oxides add to adjust the chemical and physical properties of MTA. The first developed MTA is grey MTA, and the main components are 75 wt % of type I Portland cement, 5 wt % of gypsum, and 20 wt % of bismuth oxide. However, the set grey MTA has a grey green hue, which influences the appearance of repaired tooth color. Hence, Dentsplay Co. has developed novel white MTA to replace the grey MTA. In the white MTA, the tetra-calcium aluminoferrite with deep green color is removed from Portland cement. In addition, bismuth oxide has x-ray radiopacity property. Hence, when the white MTA is used to seal roots and root-ends, the irradiation method can be used to detect the filling condition.
Although MTA has excellent filling effect, the setting time of MTA is about 3 to 4 hours. The setting time is too long, the tissue fluid or blood may cause the MTA to be washed away during the operation, which influences the sealing property and treating effect. Furthermore, the powders of the MTA are in granular form at the initial stage of blending and hard to aggregate.
In order to solve the aforementioned problems, WO 2005/039509A1 provides a dental filling material having Portland cement (i.e. the main component of MTA) as a major component, and the handling property is enhanced by adding poly(vinyl alcohol) as a viscosity enhancing substance. However, this dental filling material cannot reduce the initial setting time of Portland cement. In addition, the radiopaque substance contained in the dental filling material is bismuth oxide, so the problem of the unnatural tooth color is still unsolved.
In addition, U.S. Pat. No. 2007009858 discloses a dental filling material, which comprises CaCl2 as a hardening accelerator, and cellulose as a thickening agent, in order to improve the long initial setting time and poor handling properties of MTA. The setting time of the dental filling material can be reduced to 35 min by adding CaCl2 and cellulose. However, the particle size of CaCl2 is somewhat large (250˜1,250 μm), which causes the powders of MTA hard to be aggregated after blending MTA.
In 2007, Wiltbank et al. disclosed that the setting time of MTA can be shortened from 3˜4 hr to 35˜45 min by adding 5 wt % CaCl2, and the pH value of set MTA is about 11˜12. In addition, the setting time of MTA can be shortened to 15 min by adding 5 wt % calcium formate, and the pH value of set MTA is about 13. However, the problem of poor handling property when blending MTA is still unsolved.
In addition, in 2008, Ding et al. disclosed that the setting time of white MTA can be shortened to 25 min by adding Na2HPO4. However, Na2HPO4 can only help to accelerate initial hydration reaction, but cannot facilitate the handling property during blending MTA.
The ideal setting time is 10˜15 min. Calcium compound or Na2HPO4 can be used as a hydration accelerator to shorten the initial setting time to about 40 min is still not achieved clinical requirement. Furthermore, these methods cannot facilitate the handling property during blending MTA. Hence, if a material can combine the hydration hardening accelerator and the thickening agent, the material for treatment of endodontic can be simplified the formula and the certification of medical devices. Therefore, it is desirable to develop an additive, which can reduce the setting time of MTA hydration and facilitate the handling property at the same time.